Process for the preparation of urethanes

ABSTRACT

A process for preparing urethanes by reacting a solution of a nitrogen-containing organic compound and a hydroxyl-containing organic compound with carbon monoxide in the presence of a catalyst comprising rhodium, as a metal or compound, is disclosed. In the process of this invention, the rate of conversion and selectivity to urethane is increased by providing a rhodium catalyst comprising a polyamino ligand having at least two tertiary amino groups capable of coordinating with rhodium.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to a process for preparing urethanes by reactinga solution of a nitrogen-containing organic compound and ahydroxyl-containing organic compound with carbon monoxide in thepresence of a rhodium catalyst.

2. Description of the Art

Various patents have disclosed methods for carbonylatingnitrogen-containing organic compounds--e.g., nitro compounds, amines,azo- and azoxy compounds,--to urethanes in the presence of a platinumgroup metal-containing catalyst usually a palladium orrhodium-containing catalyst and most often a palladium or rhodiumhalide-containing catalyst. Generally, a co-catalyst (promoter) has beenneeded in combination with the platinum group metal-containing catalystin order to obtain improved rates of reaction. The vast majority ofprior art processes use, as a co-catalyst, a halide salt of a metalwhich is redox-active under the reaction conditions, usually iron, andmost often iron chlorides. The co-catalyst is used in substantial molarexcess compared to the main catalyst in order to obtain the desiredreaction rate. These large quantities of redox-active metal halides aretroublesome to separate from the reaction product and cause substantialcorrosion problems.

A few references have taught the addition of a primary amino compound(and/or related compounds, such as urea, biurets, and allophanates) tofurther improve the rate and selectivity of reactions catalyzed by aplatinum group metal compound in combination with a redox-active metalhalide-cocatalyst. U.S. Pat. No. 4,178,455 discloses that, in a processfor converting nitroaromatic to urethane catalyzed by a platinum,palladium, rhodium, or ruthenium compound and a Lewis-acid promoter, therate and selectivity are improved by adding to the reaction, an organicprimary amino compound, a urea compound, a biuret compound, anallophanate compound, or a mixture thereof. The preferred Lewis acidpromoters are redox-active metal salts, especially iron chlorides. Thispatent illustrates (by example) only palladium catalysts with ironchloride promoters. A careful study of the examples reveals that thestarting nitroaromatic and the primary amino compound (or relatedcompound) are both converted, in net, to urethane. Thus, when theprimary amino compound or urea compound contains the same aryl group asthe starting nitroaromatic compound the reported yield of urethane,based on only the nitroaromatic converted, exceeds 100%. This patentalso teaches the use of tertiary amines, e.g. pyridine, in large molarexcess compared to the palladium catalyst to prevent corrosion. See alsoU.S. Pat. No. 4,186,269 wherein a tertiary amine, e.g. pyridine, inlarge molar excess is utilized to suppress corrosion in a processutilizing a catalyst system comprising (1) palladium, ruthenium, rhodiumor compounds thereof, and (2) a Lewis Acid, e.g. ferric chloride.Similarly, U.S. Pat. Nos. 4,219,661; 4,262,130; and 4,339,592 teachpalladium catalysts with iron oxide and iron chloride co-catalysts inwhich addition of tertiary amines is one embodiment. Pyridine is thedemonstrated tertiary amine used in large molar excess relative topalladium and the stated purpose of the pyridine is to decreaseundesirable secondary reactions of the alcohol reactant. No effect ofthe tertiary amines on the activity of the catalyst towards urethanesynthesis is disclosed.

U.S. Pat. No. 4,297,501 discloses a process in which mixtures of aprimary amine and a nitroaromatic are carbonylated to urethane with aGroup VIII noble metal compound and an oxychloride compound capable ofundergoing redox reactions. Alternatively, an oxide compound capable ofundergoing redox reactions in combination with an anionic chloridecompound is used as the promoter system. Illustrated, by example, arePdCl₂ and RhCl₃, as Group VIII noble metal compounds, and the oxides andchlorides of vanadium and iron. In the preferred embodiment of U.S. Pat.No. 4,297,501, the nitroaromatic corresponds to the primary amine, andthe patent teaches the following reaction stoichiometry:

    2RNH.sub.2 +RNO.sub.2 +3CO+3R'OH→3RNHCO.sub.2 R'+2H.sub.2 O(1)

U.S. Pat. No. 4,297,501 further teaches that when nitroaromatic ispresent in excess of the 1:2 ratio relative to amine, the remainingnitroaromatic is converted to urethane by the following reactionstoichiometry:

    RNO.sub.2 +3CO+R'OH→RNHCO.sub.2 R'+2CO.sub.2        ( 2)

It can be seen from the above equations that when primary amine isinitially present, in processes which convert nitroaromatic to urethaneusing Group VIII noble metals in combination with redox-active metalhalide co-catalysts, the primary amine is, in net, consumed to also makeurethane. (See equation (1) above). Once the primary amine is consumedto low levels, any remaining nitrobenzene is converted to urethane viareaction equation (2) above. Since the primary amine is already consumedto low levels, it is no longer available to favorably influence the rateof the process according to said reaction (2).

This patent does not teach the addition of a tertiary amine to thedisclosed catalyst and promoter.

U.S. Pat. No. 4,304,922 similarly discloses a process in which mixturesof N,N'-diaryl urea and nitroaromatic are carbonylated to urethane withthe same catalyst/co-catalyst systems of U.S. Pat. No. 4,297,501.Illustrated by examples are PdCl₂, RhCl₃, IrCl₃, PtCl₄ and RuCl₃ asGroup VIII noble metal compounds. Iron oxychloride and several otherredox active metal oxides and chlorides are illustrated as co-catalysts.In examples in which redox active metal oxides are used, aniliniumhydrochloride is also added to provide active anionic chloride. In thepreferred embodiment of this patent, the N,N'-diaryl urea andnitroaromatic have the same aryl groups, and the patent teaches that thefollowing reaction stoichiometry is obtained:

    2RNHCONHR+RNO.sub.2 +3CO+5R'OH→5RNHCO.sub.2 R'+2H.sub.2 O(3)

It is known that N,N' diarylureas react with alcohols to produceurethane plus amine; see for Example U.S. Pat. No. 2,409,712, whereinthe following reaction is disclosed:

    RNHCONHR+R'OH→RNHCO.sub.2 R'+RNH.sub.2              ( 4)

It can be seen that once this occurs under the reaction conditions, thesame process as U.S. Pat. No. 4,297,501 is obtained according toequation (1) above. (Twice equation (4) plus equation (1) equalsequation (3)). It can further be seen that both N,N'-diaryl urea andarylamine are, in net, consumed in the process to make urethane. Example11 of U.S. Pat. No. 4,304,922 illustrates that when RhCl₃ is used ascatalyst in combination with iron oxychloride as co-catalyst,nitrobenzene and N,N'-diphenylurea (1:2 molar ratio) are both consumed(100% and 99% conversion, respectively) to give urethane product 99%selectivity based on nitrobenzene plus N,N'-diphenylurea).

Again, like U.S. Pat. No. 4,297,501 there is no teaching of theadvantage of adding a tertiary amine to the disclosed process.

Japan Kokai No. 55-7227 discloses a process in which molecular hydrogenis added, to a process for carbonylating nitroaromatic, in the presenceof a palladium catalyst, to increase the reaction rate. The descriptionof the invention specifies a palladium catalyst, accompanied bypromoters such as tertiary amines, iron and vanadium compounds, andchlorine ions. All illustrated examples use a supportedpalladium-selenium on carbon catalyst promoted with pyridine and eitherFeCl₂ or VOCl₃ (these are redox-active metal chlorides). The patentteaches that the addition of hydrogen causes hydrogenation of a fractionof the nitroaromatic to generate the corresponding primary arylamine insitu. The process is thus generically similar to that of U.S. Pat. No.4,178,455, discussed above, which illustrates by example the addition ofprimary arylamine to a reaction with a supported palladium catalystpromoted with FeCl₃. Thus, it may be concluded that primary aminegenerated from hydrogen will in net be consumed in the reaction to makeurethane. Indeed, Japan Kokai No. 55-7227 teaches that any primary amineremaining at the end of a reaction can be returned to another reactionwith more nitroaromatic, in which case the primary amine is easilyconverted to urethane.

In U.S. Pat. No. 4,474,978 a process is disclosed for converting anitroaromatic to a urethane in the presence of a primary amine and acatalyst system based on palladium complexed with Group VA-chelateligands, including bis-tertiary amino-containing ligands. The patentteaches that the redox active metal chloride and related co-catalystsare no longer needed when the above ligands are used. But, this patentdoes not suggest the use of rhodium in combination with said ligands andalso teaches that the primary amine and/or urea are co-converted withthe nitroaromatic to urethane. Thus, the process, in net, consumes addedamine or urea. See the examples disclosed in the patent.

Thus, it is clear that, in the processes cited above, as the primaryamine and/or urea compound is converted, in net, to urethane, itsconcentration decreases and its effects on reaction rate and selectivitymust also decrease. Eventually, as nitroaromatic continues to beconverted, either in a batch process or in a continuous process (withrecycle of the remaining amine), the primary amine will be consumed to alow concentration. In order to maintain the improved rates andselectivities, which are obtained by the original addition of primaryamine, urea, hydrogen, etc., it is necessary to provide additionalprimary amine, urea, hydrogen, etc. as the primary amine is consumed.

A few references teach the use of rhodium catalysts, in the absence of aredox-active metal co-catalysts, for the carbonylation ofnitrogen-containing organic compounds to urethanes. However, thesereferences do not teach the initial addition of primary amines, ureas,hydrogen, etc. to obtain improved activity. For example, U.S. Pat. No.3,338,956 discloses a metal carbonyl catalyst of Group VIA, VIIA, orVIIIA for this reaction. The only such catalyst exemplified, however, isrhodium chlorocarbonyl and the rates of reaction are relatively slow.Moreover, this reference does not teach the advantages of adding atertiary amine to the disclosed carbonylation process.

U.S. Pat. No. 3,993,685 teaches the addition of tertiary amines,especially pyridine, to platinum group metal catalysts to obtainimproved activity in the absence of redox-active metal co-catalysts.Rhodium chloride and hydridocarbonyltris(triphenylphosphine) rhodium incombination with pyridine are exemplified. In this reference it isclearly pointed out that a high concentration or excess of the tertiaryamine is desirable, the tertiary amine serving as both catalyst andsolvent. (Note that the suggested tertiary amines are not bis(tertiaryamines)).

U.S. Pat. No. 4,052,437 discloses the use of rhodium oxide as catalyst,preferentially in nitrilic solvent. Rh₆ (CO)₁₆ as a catalyst is alsoexemplified in this patent. There is no suggestion that the initialaddition of a primary aryl amine to the process disclosed in this patentwould improve the rate. Also, there is no suggestion of the advantage ofadding a tertiary amine to the catalyst disclosed therein.

An article in the Journal of Organic Chemistry 37, 2791 (1972) describesa reaction in which nitro-benzene in the presence of ethanol iscarbonylated in low yield (<10%) to urethane with a catalyst comprisingRh₆ (CO)₁₆ in pyridine solvent. The major product was aniline. Again,like U.S. Pat. No. 3,993,685, above, the pyridine is used in highconcentration or excess to enable its function as a solvent for thereaction.

None of the above cited art, which discloses the use of rhodiumcatalysts (in the absence of redox-active metal co-catalysts) for thecarbonylation of nitro-organics to urethanes, discloses the initialaddition of primary amine, urea, hydrogen, etc. Moreover, the effect ofinitially adding primary amine to such catalysts is not predictable.Finally, the result obtained by adding a primary amine to a rhodiumcatalyst system essentially free from redox-active metal components, issubstantially different from the result obtained when a primary amine isadded to either Group VIII metal catalysts (including rhodium andpalladium) in the presence of redox active metal co-catalysts or certainpalladium catalysts in the absence of redox active metal co-catalysts.

There are references, which disclose the conversion of nitroaromatic tourethane in the presence of a platinum metal catalysts and in which theprimary amine is not in net consumed. See copending patent applicationsSer. Nos. 532,784; 532,785 and 707,885, filed Sept. 16, 1983, Sept. 16,1983 and Mar. 4, 1985, respectively. All three applications were filedin the names of Grate, Hamm, and Valentine and all are entitled "Processfor the Preparation of Urethanes". Also, see patent application Ser. No.744,951, filed June 17, 1985, in the names of Grate and Hamm, andentitled "Process for the Preparation of Urethanes."

It is an object of this invention to provide a process for theconversion of nitro-aromatic to urethane in good rate and selectivity,without requiring continual addition of primary amine, urea, hydrogen,etc. to maintain the rate and selectivity.

It is a further object of this invention to effectively carry out theabove process in the absence of redox-active metal halide co-catalysts.

It is also an object of this invention to effectively carry out theabove process in the absence of a large molar excess of tertiary amineas compared to the catalyst.

SUMMARY OF THE INVENTION

It has now been surprisingly found that, in a process for carbonylatingnitrogen-containing organic compounds to urethanes, in the presence of arhodium catalyst, a substantial improvement in the rate and selectivityof the reaction may be obtained by providing a poly amino ligand havingat least two tertiary amino groups capable of coordinating with rhodium.Moreover, when a primary amine is added to the reactant solution tofurther improve rate and selectivity, the primary amine is not in netconsumed during the reaction. Thus, in a batch process, the effects ofthe added primary amine do not diminish as the reaction proceeds. In acontinuous process, the primary amine can be constantly recycled and nofurther addition of primary amine, urea, hydrogen, etc. is needed tomaintain the desired rate and selectivities.

While not wishing to be bound by theory, it appears that, in the rhodiumcatalyzed carbonylation of the above nitrogen-containing organiccompound to the corresponding urethane, in the absence of a redox-activemetal halide co-catalyst, the urethane is produced by oxidativecarbonylation of the corresponding primary amine. This oxidativecarbonylation also provides hydrogen atom equivalents for the reductionof the nitrogen-containing organic compound to the primary amine. Thesereactions which are illustrated below (wherein [H] represents therhodium hydrogen carrier) must be effectively coupled to provide thedesired selectivity to the urethane. ##STR1##

Thus, the primary amine (illustrated by aniline) is an intermedite inthe formation of urethane from the nitrogen-containing organic compound,but is not in net produced or consumed by the desired net reaction.

It has been found that the rate and selectivity of reaction, obtainedwith rhodium catalysts comprising a polyamino ligand having at least twotertiary amino groups capable of coordinating with rhodium in theabsence of redox-active metal halide co-catalyst, are improved when theprimary amine is initially present in the reaction. It has been furtherfound that the primary amine is not in net consumed and the desiredreaction stoichiometry is obtained even when primary amine is initiallyadded to the reaction. The initial amount of primary amine and itsfavorable effects on the rate and selectivity of the reaction persistfor the conversion of an indefinite amount of nitrogen-containingorganic compound.

The primary amine can be provided directly or by the in sutu alcoholysisof a urea, biuret, or allophanate compound. Urea is alcoholyzed to formamine and urethane:

    RNHCONHR+R'OH→RNH.sub.2 +RNHCO.sub.2 R'

Biurets and allophanates similarly provide primary amine by alcoholysisunder the reaction conditions.

In a carbonylation reaction wherein no primary amine, urea, biuret, orallophanate is present, initially, a fraction of the nitrogen-containingcompound (e.g. nitrobenzene) can be reduced to the primary amine(aniline) by added hydrogen. It has been found that the reduction of thenitrogen-containing organic compound to a primary amine in the presenceof hydrogen is rapid and provided that the molar ratio of hydrogen tothe nitrogen-containing organic compound is less than 1, the remainderof the nitrogen-containing organic compound is converted to urethane bythe desired reaction stoichiometry. The primary amine may also beprovided in situ by the addition of water, in which case a fraction ofthe nitrogen-containing compound is reduced to primary amine by hydrogenequivalents obtained from shifting water and carbon monoxide to carbondioxide.

In the initial absence of primary amine, hydrogen or water, the hydrogenequivalents required to initially reduce nitrogen-containing organiccompound to the primary amine are derived by dehydrogenation of thealcohol. (In the scheme illustrated below R represents a hydrogen orhydrocarbyl radical.) ##STR2##

DECTAILED DESCRIPTION OF THE INVENTION

The nitrogen-containing organic compound useful in the process of thisinvention will contain at least one non-cyclic group in which a nitrogenatom is directly attached to a single carbon atom and through a doublebond to oxygen or another nitrogen atom. The nitrogen-containing organiccompound is selected from the group consisting of nitro, nitroso, azoand azoxy compounds.

Examples of suitable nitrogen-containing organic compounds for use inthe process of this invention are compounds represented by the generalformulae:

    R.sub.1 (NO.sub.x).sub.y                                   I

and

    R.sub.1 --RN═N (O).sub.z --R.sub.2                     II

wherein R₁ and R₂ are radicals independently selected from the groupconsisting of C₁ to C₂₀ hydrocarbyl radicals and substituted derivativesthereof, x is an integer of from 1 to 2, y is an integer of from 1 to 3,and z is an integer of from 0 to 1. The substituted hydrocarbyl radicalmay include hetereo atoms selected from the group consisting of halogen,oxygen, sulfur, nitrogen and phosphorus atoms.

The nitrogen-containing compounds represented by formula I include nitrocompounds (wherein x is 2) and nitroso compounds (wherein x is 1).Suitable nitro compounds are mononitro compounds such as nitrobenzene,alkyl and alkoxy nitrobenzenes wherein the alkyl group contains up to 10carbon atoms, aryl and aryloxy nitrobenzenes, wherein the aryl group isphenyl, toyl, naphthyl, xylyl, chlorophenyl, chloronitrobenzenes,aminonitrobenzenes, carboalkoxyamino nitrobenzenes wherein the alkoxygroup has up to 10 carbon atoms, aryl and aryloxy dinitrobenzenes,trinitro compounds such as trinitrobenzene, alkyl andalkoxytrinitrobenzenes, aryl and aryloxytrinitrobenzenes, thesubstituents being any of those already mentioned andchlorotrinitrobenzenes as well as similarly substituted mono andpolynitro derivatives of the naphthalene, diphenyl, diphenylmethane,anthracene and phenanthrene series. Substituted or unsubstitutedaliphatic nitro compounds such as nitromethane, nitrobutane,2,2'-dimethyl nitrobutane, nitrocyclopentane, 3-methylnitrobutane,nitrooctadecane, 3-nitropropene-1, phenyl nitromethane, p-bromophenylnitromethane, p-methoxy phenyl nitromethane,dinitroethane,dinitrohexane, dinitrocyclohexane, di-(nitrocyclohexyl)-methane are alsosuitable. The above nitro compounds may include more than one of theabove substituents (in addition to the nitro group(s) such as innitroaminoalkylbenzenes, nitroalkylcarboalkoxyamino benzenes, etc. Fromthis group of nitro compounds nitrobenzene, nitrotoluene,dinitrobenzene, dinitrotoluene, trinitrobenzene, trinitrotoluene,mononitronaphthalene, dinitronaphthalene, 4,4'-dinitrodiphenylmethane,nitrobutane, nitrocyclohexane, p-nitrophenylnitromethane,dinitrocyclohexane, dinitromethylcyclohexane, dinitrocyclohexylmethane,nitroaminotoluene and nitrocarboalkoxyaminotoluene are preferred and inparticular aromatic nitro compounds especially 2,4- and2,6-dinitrotoluenes, meta and para dinitrobenzenes, and5-nitro-2-methyl-carboalkoxyamino-, 2-nitro-5-methyl-carboalkoxyamino-,and 3-nitro-2-methyl-carboalkoxyamino benzenes.

Examples of suitable nitroso compounds are the aromatic nitrosocompounds such as nitrosobenzene, nitrosotoluene, dinitrosobenzene,dinitrosotoluene and the aliphatic nitroso compounds such asnitrosobutane, nitrosocyclohexane and dinitrosomethylcyclohexane.

The nitrogen-containing compounds represented by Formula II include bothazo compounds (wherein z is 0) and azoxy compounds (wherein z is 1).Suitable compounds represented by Formula II include azobenzene,nitroazobenzne, chloroazobenzene, alkyl or aryl substituted azobenzene,azoxybenzene, nitroazoxybenzene, chloroazoxybenzene, etc.

The hydroxy-containing organic compounds for use in the process of thisinvenntion include compounds represented by the general formula

    R.sub.1 (OH).sub.y

    III

wherein R₁ and y are defined above.

Hydroxy compounds suitable for use in the process of the presentinvention may be, for example, mono- or polyhydric alcohols containingprimary, secondary or tertiary hydroxyl groups as well as mono- andpolyhydric phenols. Mixtures of these hydroxy compounds may also beused. The alcohols may be aliphatic or aromatic and may bear othersubstituents in addition to hydroxyl groups but the substituents should(except as hereinafter described) preferably be non-reactive to carbonmonoxide under the reaction conditions. Especially suitable compoundsare phenol and monohydric alcohols such as methyl, ethyl, n- andsec-propyl, n-, iso, sec-and tert butyl, amyl, hexyl, lauryl, cetyl,benzyl, chlorobenzyl and methoxybenzyl alcohols as well as diols such asethylene glycol, diethylene glycol, propylene glycol and dipropyleneglycol, triols such as glycerol, trimethylol propane, hexanetriol,tetrols such as pentaerythritol and the ethers of such polyols providingthat at least one hydroxyl group remains unetherified. The etherifyinggroup in such ether alcohols normally contains up to 10 carbon atoms andis preferably an alkyl, cycloalkyl or aralkyl group which may besubstituted with, for example, a halogen or an alkyl group.

The most preferred hydroxyl-containing organic compound for use in theprocess of this invention is methyl alcohol or a similar lower alkanol,e.g. a C₁ to C₅ alcohol.

The process of this invention includes the use of any mixture of nitrocompounds, nitroso compounds, azo or azoxy compounds with any mixture ofhydroxy compounds and also the use of compounds containing bothfunctions, i.e. hydroxynitro compounds, hydroxynitroso compounds,hydroxyazo and hydroxyazoxy compounds such as 2-hydroxynitroethane,2-hydroxynitrosoethane, nitrophenols, nitronaphthols, nitrosophenols,nitrosonaphthols, hydroxyazobenznes and hydroxyazoxybenzenes. Mixturesof these nitrogen-containing compounds may also be used.

This process of the invention has been found to proceed most smoothly togive the highest yields when employing nitro compounds. It isaccordingly preferred to use nitro compounds rather than nitroso, azo orazoxy compounds.

The catalyst utilized in the process of this invention may be selectedfrom the group consisting of rhodium salts, e.g. the halides, nitrate,sulfate, acetate, formate, carbonate, etc. and rhodium complexes(especially rhodium carbonyl complexes) including ligands capable ofcoordinating with the rhodium atom. The complex may include one or morerhodium atoms and suitable ligands may include carbon-carbon unsaturatedgroups as in ethylene, isobutylene, cyclohexene, norbornadiene,cyclooctatetraene. Other suitable ligands include acetylacetonate(acac), hydrogen atoms, carbon monoxide, nitric oxide, alkyl-radicals,alkyl or aryl nitriles or isonitriles, nitrogen-containing heterocycliccompounds such as pyridine, piperidine, and organo phosphines, arsinesor stilbines.

The rhodium catalyst further comprises a polyamino ligand having atleast two tertiary amino groups capable of coordinating with rhodium.For example, such polyamino ligand may be selected from the group ofcompounds represented by the general formula: ##STR3## wherein R₃, R₄,R₇ and R₈, which may be the same or different, each represent an alkyl,aryl, alkaryl or aralkyl group which may be substituted by one or moreinert substituents or R₃ and R₄ and/or R₇ and R₈ may form a ringstructure together with the atom N to which they are attached; R₅ andR₆, which may be the same or different, each represent a hydrogen atomor a lower alkyl group and may form a ring structure together with theatom N and R₃, R₄, R₇ and/or R₈ and n is an integer, preferably n variesfrom 1 to about 5, e.g. 1 to 3.

Examples of ligands according to the general formula are1,2-bis(diethylamino)ethane 1,2-bis(dimethylamino)propane,1,2-bis(dimethylamino)ethane, 1,2-bis(di-t-butylamino)ethane,1,2-bis(diphenylamino)ethane, 1,2-bis(diphenylamino)propane,1,2-bis(diphenylamino)butane, 2,2'-bipyridine, 2,2'-biquinoline,bispyridylglyoxal, and 1,10-phenanthroline and derivatives thereof.Preference is given to the use of 2,2'-bipyridine and1,10-phenanthroline.

The rhodium catalyst is preferably utilized as a homogeneous catalystand therefore one criteria for the selection of the rhodium compound isits solubility under the conditions of reaction in the mixture of thenitrogen-containing organic compound, the hydroxyl-containing organiccompound and the primary amino compound. The rhodium compound is alsoselected with a view toward the catalytic activity of the compound.

The rhodium compound comprising a polyamino ligand may be preformed orformed in situ in the reaction solution by separately dissolving arhodium compound and a polyamino ligand. Since the catalyst is utilizedin very low concentration, it is preferred that the compound ispreformed to ensure that the polyamino ligand will be coordinated withthe rhodium during the reaction.

The rhodium catalyst may be used in mixture with co-catalysts orpromoters so long as the co-catalyst, unlike the redox-active metalhalide co-catalysts of the prior art, does not change the reactivity ofthe catalyst system to consume added amines. Mono-tertiary amines areone class of suitable promoters for the rhodium catalysts of thisinvention. Suitable mono-tertiary amines are those described in U.S.Pat. No. 3,993,685 herein incorporated by reference.

The primary amine compound utilized in one embodiment of this inventionmay be selected from the group consisting of compounds represented bythe general formula:

    R.sub.1 (NH.sub.2).sub.Y                                   IV

wherein R₁ and Y are as defined above. Examples of such primary aminesinclude methylamine, ethylamine, butylamine, hexylamine,ethylenediamine, propylenediamine, butylenediamine, cyclohexylamine,cyclohexyldiamine, aniline, p-toluidine, o-m-and p-diaminobenzenes,aminomethylcarbanilic acid esters, especially the 5-amino-2-methyl-,2-amino-5-methyl-, and 3-amino-2-methyl carboalkoxyaminobenzenes,wherein said alkoxy group has up to 10 cabon atoms, o-, m- andp-nitroanilines, nitroaminotoluenes, especially those designated above,o-and p-phenylenediamine, benzylamine, o-amino-p-xylene,1-aminophthaline, 2,4-and 2,6-diaminotoluenes, 4,4'-diaminodibenzyl, bis(4-aminophenyl) thioether, bis (4-aminophenyl) sulfone,2,4,6-triaminotoluene, o-, m-and p-chloroanilines, p-bromoaniline,1-fluoro-2,4-diaminobenzene, 2,-4-diaminophenetole, o,-m- andp-aminoanisoles, ethyl p-aminobenzoate, 3-aminophthalic anhydride, etc.These primary amino compounds may be used alone or in combination.

Among the above-enumerated primary amino compounds, those which can bederived from the starting nitro compound are preferred. For example,when nitrobenzene is used as the starting aromatic nitro compound,aniline is preferred. Similarly, 2-amino-4-nitrotoluene,4-amino-2-nitrotoluene, and 2,4-diaminotoluene are preferably used whenthe starting aromatic nitro compound is 2,4-dinitrotoluene, while2-amino-6-nitrotoluene, and 2,6-diaminotoluene are preferably used whenthe starting aromatic nitro compound is 2,6-dinitrotoluene.

The primary amine compound can be provided by the in-situ decompositionof the corresponding urea or biuret as represented by compounds havingthe general formulae: ##STR4## respectively, wherein R₁ is as definedabove. Of course, since the above urea and biuret will comprise morethan one radical, R₁ may represent different radicals in the samecompound. That is non-symmetrical ureas and biurets, e.g. are within thescope of the invention.

In the process of this invention, no particular limitation is placed onthe amount of primary amine used. However, it is preferably used in anamount equal to from 0.1 to 100 moles per gm-atom of nitrogen in thenitrogen-containing organic compound.

The process of the invention may be carried out in the absence ofsolvent but the use of a solvent is not precluded. Suitable solventsinclude, for example, aromatic solvents such as benzene, toluene,xylene, etc.; nitriles such as acetonitrile, benzonitrile, etc.;sulfones such as sulfolane, etc.; halogenated aliphatic hydrocabons suchas 1,1,2-trichloro-1,,2,2,-trifluoroethane, etc.; halogenated aromatichydrocarbons such as monochlorobenzene, dichlorobenzene,trichlorobenzene, etc.; ketones; esters; and other solvents such astetrahydrofuran, 1,4-dioxane, 1,2-dimethoxyethane, etc.

In carrying out the process of the invention, the hydroxyl-containingorganic compound and carbon monoxide may be used in amounts equal to atleast 1 mole per gm-atom of nitrogen in the nitrogen-containingcompound. Preferably the hydroxyl-containing organic compound is used inexcess and functions as a solvent as well as a reactant.

The amount of the rhodium compound used as the catalyst may vary widelyaccording to the type thereof and other reaction conditions. However, ona weight basis, the amount of catalyst is generally in the range of from1×10⁻⁵ to 1 part, and preferably from 1×10⁻⁴ to 5×10⁻¹ parts, pergram-atom of nitrogen in the starting nitrogen-containing organiccompound when expressed in terms of its metallic component.

The reaction temperature is generally held in the range of 80° to 230°C., and preferably in the range of from 100° to 200° C.

The reaction pressure, or the initial carbon monoxide pressure, isgenerally in the range of from 10 to 1,000 kg/cm² G, and preferably from30 to 500 kg/cm² G.

The reaction time depends on the nature and amount of thenitrogen-containing organic compound used, the reaction temperature, thereaction pressure, the type and amount of catalyst used, the type ofreactor employed, and the like, but is generally in the range of from 5minutes to 6 hours. After completion of the reaction, the reactionmixture is cooled and the gas is discharged from the reactor. Then, thereaction mixture is subjected to any conventional procedure includingfiltration, distillation, or other suitable separation steps, wherebythe resulting urethane is separated from any unreacted materials, anyby-products, the solvent, the catalyst, and the like.

The urethanes prepared by the process of the invention have wideapplications in the manufacture of agricultural chemicals, isocyanates,and polyurethanes.

The invention is more fully illustrated by the following examples.However, they are not to be construed to limit the scope of theinvention.

In each of the following examples, the reaction was conducted in batchmode in a 300 ml stainless steel autoclave reactor equipped with astirring mechanism which provides constant dispersion of the gas throughthe liquid solution. Heating of the reaction is provided by ajacket-type furnace controlled by a proportioning controller. Theautoclave is equipped with a high pressure sampling system for removalof small samples of the reaction solution during the reaction in orderto monitor the reaction progress. Reaction solutions were prepared andmaintained under anaerobic conditions. Reaction samples were analyzed bygas chromatography.

The following examples are shown for the purpose of illustration onlyand should not be deemed as limiting the scope of the invention.

EXAMPLE 1

0.103 g (0.400millimole) dicarbonylacetylacetonato rhodium and 0.072 g(0.400 millimole) 1,,10-phenanthroline were mixed in methanol, giving adeep purple-black solution. 12.31 g (0.100 mole) nitrobenzene, 4.66 g(0.050 mole) aniline, 2.68 g t-butylbenzene (internal standard) andadditional methanol were added to give a total solution volume of 75 ml.The solution was placed in the reactor vessel and the gas volume in thereactor was replaced with carbon monoxide at 1000 psig at ambienttemperature. The reactor contents were then heated to 160° C. over 1.5hours. On reaching 160° C., approximately 50% of the nitrobenzene wasconverted. After 2.0 hours at 160° C., nitrobenzene conversion wascomplete and the solution contained 0.080 mole methyl N-phenyl carbamate(80% selectivity based on nitrobenzene). 0.065 mole aniline, 0.006 moleN-methylene aniline, and 0.001 mole N-methylaniline (summed to 20%selectivity to additional aniline based on nitrobenzene).

EXAMPLE 2

The procedure was the same as for Example 1 with the exception that0.078 g (0.400 milligram-atoms Rh) [Rh(CO)₂ Cl]₂ was used as the rhodiumsource. Approximately 40% of the nitrobenzene was converted as thereactor contents were heated to 160° C. After 3.0 hours at 160° C.,nitrobenzene conversion was complete and the solution contained 0.089mole methyl N-phenyl carbamate (89% selectivity based on nitrobenzene)and 0.058 mole aniline (8% selectivity to additional aniline based onnitrobenzene).

EXAMPLE 3

The procedure was the same as for Example 1 with the exception that0.105 g (0.400 millimole) RhCl₃.3H₂ O was used as the rhodium source.After 19 hours at 160° C., the solution contained 0.085 molenitrobenzene (15% nitrobenzene conversion), 0.015 mole methyl-N-phenylcarbamate (100% selectivity to urethane based on nitrobenzene), 0.045mole aniline and 0.004 mole N-methylaniline.

EXAMPLE 4

The procedure is the same as for Example 1 with the exception that therhodium-phenanthroline catalyst was prepared as follows: Methanolsolutions of 0.0389 g (0.200 milligram-atoms Rh) [Rh(CO)₂ Cl]₂ and0.0514 g (0.200 millimole) Ag(CF₃ SO₃) were mixed. AgCl was removed byfiltration, leaving a yellow homogeneous solution. A methanol solutionof 0.0360 g (0.200 millimole) 1,10-phenanthroline was then added,,giving a black suspension. Aniline, nitrobenzene, t-butylbenzene, andadditional methanol were then added and the reaction was conductedaccording to the procedure of Example 1. After 16 hours at 160° C.,nitrobenzene conversion was complete and the solution contained 0.076mole methyl N-phenyl carbamate (76% selectivity based on nitrobenzeneand 0.067 mole aniline (17% selectivity to additional aniline based onnitrobenzene).

EXAMPLE 5

The procedure was the same as for Example 1 with the exception thataniline was omitted from the initial reaction solution. As the reactorcontents heated to 160° C., approximately 30% of the nitrobenzene wasconverted. Complete nitrobenzene conversion required 5.5 hours at 160°C. and yielded 0.068 mole methyl N-phenyl carbamate (68% selectivity),0.022 mole aniline, 0.007 mole N-methylene aniline, and 0.001 mole(N-methylaniline (summed to 30% selectivity to aniline).

EXAMPLE 6

The procedure was the same as for Example 1 with the exception thatethanol was substituted for methanol on an equal volume basis. After 2.0hours at 160° C., the solution contained 0.055 mole nitrobenzene (45%nitrobenzene conversion), 0.020 mole ethyl-N-phenylcarbamate (44%selectivity based on nitrobenzene), and 0.074 mole aniline (53%selectivity to additional aniline based on nitrobenzene).

What is claimed is:
 1. A process for converting a nitrogen-containingorganic compound, selected from the group consisting of nitro, nitroso,azo, and azoxy compounds, into the corresponding urethane, by reacting asolution, comprising said nitrogen-containing organic compound and ahydroxyl-containing organic compound, with carbon monoxide, whichcomprises the step of:(a) contacting the solution with carbon monoxide,in the presence of a rhodium catalyst comprising a polyamino ligandhaving at least two tertiary amino groups capable of coordinating withrhodium at conditions sufficient to convert said nitrogen-containingorganic compound into the corresponding urethane, wherein said polyaminoligand is selected from the group of compounds represented by thegeneral formula: ##STR5## wherein R₃, R₄, R₇, and R₈, which may be thesame or different, each represent an alkyl, aryl, alkaryl or aralkylgroup which may be substituted by one or more inert substituents or R₃and R₄ and/or R₇ and R₈ may form a ring stucture together with the atomN to which they are attached; R₅ and R₆, which may be the same ordifferent, each represent a hydrogen atom or a lower alkyl group and mayform a ring structure together with the atom N and R₃, R₄, R₇ and/or R₈and n is an integer.
 2. The process of claim 1 wherein said polyaminoligand is selected from the group consisting of 2,2-bipyridine and1,10-phenanthroline.
 3. The process of claim 1 wherein saidnitrogen-containing organic compound is a nitro compound.
 4. The processof claim 3 wherein said nitro compound is an aromatic nitro compound. 5.The process of claim 1 further comprising the step of providing aprimary amine in said solution.
 6. The process of claim 5 wherein saidnitrogen-containing compound is an aromatic nitro compound.
 7. Theprocess of claim 6 wherein said primary amine is an aromatic amine. 8.The process of claim 7 wherein said aromatic amine corresponds to saidaromatic nitro compound.
 9. The process of claim 5 wherein said primaryamine is provided by reducing said nitrogen-containing compound withhydrogen in said solution.
 10. The process of claim 5 wherein saidprimary amine is provided by reducing said nitrogen-containing compoundwith hydrogen equivalents derived from the rhodium-catalyzed water-gasshift reaction.
 11. The process of claim 5 wherein said aromaticnitro-compound is selected from the group consisting of nitrobenzene,nitroanisole, dinitrotoluene, nitromesitylene, bis(4-nitro-phenyl)methane, nitroaminotoluene and nitrocarboalkoxyaminotoluene.
 12. Theprocess of claim 7 wherein said amine is selected from the groupconsisting of p-toluidine, aniline, diaminotoluene, bis (4-aminophenyl)methane, aminonitrotoluene, and aminomethylcarboalkoxybenzene.
 13. Theprocesss of claim 5 wherein said amine is provided by decomposing a ureaor biuret in-situ.
 14. The process of claim 1 wherein saidnitro-containing organic compound is converted into the correspondingurethane, by reacting said solution with carbon monoxide at atemperature of from about 100° C. to 200° C. and a carbon monoxidepressure in the range of from 30 to 500 kg/cm² G.
 15. The process ofclaim 14 wherein said polyamino ligand is 2,2-bipyridine.
 16. Theprocess of claim 1,4 wherein said polyamino ligand is1,10-phenanthroline.
 17. The process of claim 1 wherein said rhodiumcatalyst is selected from the group consisting of rhodium carbonylcomplexes.
 18. The process of claim 7 wherein said rhodium carbonylcomplex is selected from the group consisting ofdicarbonyloacetylacetonato rhodium, [Rh(CO)₂ Cl]₂ and Rh₆ (CO)₁₆. 19.The process of claim 1 wherein said hydroxyl-containing organic compoundis methanol.
 20. The process of claim 1 wherein said hydroxyl-containingorganic compound is ethanol.
 21. The process of claim 14 wherein saidhydroxyl-containing organic compound is methanol.
 22. The process ofclaim 14 wherein said hydroxyl-containing organic compound is ethanol.23. The process of claim 21 wherein said polyamino ligand is1,10-phenanthroline.
 24. The process of claim 1 wherein n is 2 or more.